This invention relates to a cryogenic refrigerator of a rotary type suitable for use in the field of cryoelectronics.
There are known various types of cryogenic refrigerators which are based on Stirling, Solvay or Gifford-McMahon thermodynamic priciples for production of cryogenic temperatures. They are provided with a compressor and an expander with a regenerator interposed therebetween, and are so arranged that cyclin adiabatic expansion in the expander of the working gas such as helium compressed by the compressor causes a continuous temperature drop in the expander and the regenerator, thereby providing a cryogenic temperature.
In the majority of the known refrigerators of the above-mentioned type, the compressor and the expander are of a reciprocating piston type, that is, of the type that a piston is reciprocated within a cylinder for compression or expansion of the working gas.
The compressor or the expander of the reciprocating type, however, has the following disadvantages.
While the device is running, the reciprocating piston causes considerable mechanical vibration and noise to occur and due to low durability of the piston seal the device has a relatively short operation life. Also, in order to make the refrigerator compact in size and light in weight without appreciable reduction of the refrigerating capacity, it is necessary to increase the number of cycles per unit period of time. However, such increase in the number of cycles is accompanied by a corresponding increase in the accelaration of the reciprocating piston and its associated members, with a resulting increase in the load on the cam, crank and other members for controlling the motion of the piston. This means that if the compressor, the expander or the regenerator is to be made compact or small in size, for compensation of the decrease in the capacity by a higher speed of operation a greater mechanical strength is required of the movable members of the device, with a resulting increase in the size of the device. This certainly is a contradiction or dilemma and by using a compressor and/or an expander of the reciprocating piston type it is practically impossible to make the refrigerator compact in size without appreciable lowering of its performance. Moreover, a great acceleration acting on the piston or its associated members causes magnetic noise to occur so that the refrigerator becomes unsuitable for cooling cryoelectronic devices such as a SQUID.
The object of the invention is therefore to provide a cryogenic refrigerator of a rotary type which has completely eliminated the above-mentioned and other disadvantages of the prior art devices.
The invention will be described in detail with reference to the accompanying drawings.